1. Field of the Invention
The present invention relates generally to a video signal recording apparatus and, more particularly, to a video signal recording apparatus having an interval recording mode for recording a predetermined amount of video signal at predetermined time intervals.
2. Description of the Related Art
In recent years, a demand for high-density recording has been increasing in the field of magnetic recording. To meet such a demand, there is provided, for example, a video tape recorder (VTR) of the type which is capable of effecting magnetic recording of high density by transporting a magnetic tape at a reduced speed. However, a VTR provided with a fixed head for recording an audio signal has the disadvantage that if an audio signal is recorded while simply transporting a magnetic tape at a reduced speed, no large relative speed is obtained between the head and the tape and the quality of reproduced sound is degraded. For this reason, a method has been adopted in which the length of each track scanned by a rotary head is extended with respect to the track length used in the conventional art and a PCM audio signal which is compressed along its time axis is sequentially recorded in the additional portion of each extended track.
By way of example, such a method will be explained with reference to a VTR of the rotary 2-head helical scan type. As shown in FIG. 1, a magnetic tape 31 is wrapped around a rotary cylinder 32 through an angle of (180+.theta.) degrees or more. As shown in FIG. 2, each track includes a video signal recording area 34 corresponding to the rotation of the rotary cylinder 32 through 180 degrees and a PCM audio signal recording area 33 corresponding to the rotation of the rotary cylinder 32 through .theta. degrees. Rotary heads 30A and 30B alternately trace successive tracks to record a PCM audio signal which is compressed along its time axis in the PCM audio signal recording area 33 of each track as well as a video signal for one field per track in the video signal recording area 34 of each track.
A method of recording a digital signal representative of a still image in a digital signal recording area instead of such a PCM audio signal has been proposed as an applied example of the aforesaid method of recording a digital signal in one area while recording a video signal in another area. Since the amount of information of a still image is comparatively small, it is possible to record the entire still-image information on a magnetic tape by using the PCM audio signal recording areas of a plurality of tracks. According to this method, not only is it possible to realize still-image photography utilizing a photographic apparatus and a recording medium which are identical to those used for motion-image photography, but it is also possible to record and/or reproduce a high-quality still image. The quality of the still image reproduced by this method is higher than that of a still image obtainable by repeatedly reproducing a video signal from the same track on a magnetic tape in a VTR while keeping the magnetic tape in a stopped state.
It is also known that a camera-integrated VTR has been proposed which is composed of such a recording device and a camera and which is capable of recording not only a motion image but also a still image.
If a still image is recorded in the above-described manner, the time required to record one still image will change variously due to conditions such as the sampling frequency at which a video signal is sampled, the number of bits for quantization, the rate of information compression by a high-efficiency encoding circuit, recording density, and the kind of still image, i.e., whether a frame image or a field image. As will be described later, the time required to record one still image changes between 0.5 seconds and 11.1 seconds.
As is known, camera-integrated VTRs having interval photography modes are provided as manufactured products. The interval photography mode is a mode in which a video signal for a predetermined time, for example, a fraction of a second to several seconds is recorded at predetermined time intervals, for example, at intervals of several seconds to several minutes. In general, a manufactured-product version of such a camera-integrated VTR is arranged in such a manner that the aforesaid predetermined time interval (photography interval) or the aforesaid predetermined time (photography time) can be arbitrarily selected from a plurality of set values.